Existing railroad locomotives are typically powered by diesel electric systems in which a diesel engine drives an electric generator to produce electric power to energize electric motors which propel the drive wheels of the locomotive. Recently, there has been an increased interest in creating a modified locomotive in which electric power is supplied by an energy storage device such as a battery that is connected to be charged by a generator on an as needed basis using a fuel powered engine such as a diesel engine, gas turbine, Liquid Natural Gas (LNG) engine, gasoline engine, or even a hydrogen fueled Internal Combustion Engine (ICE). Such an approach is known in the automobile industry as a “hybrid” vehicle. These hybrid vehicles have the advantage of increased fuel efficiency and reduced pollution.
One attempt to create a hybrid locomotive is disclosed in U.S. Pat. No. 6,308,639 (the '639 patent). The '639 patent discloses a locomotive in which a gas microturbine generator provides recharging current for a battery. The disclosed locomotive has a conventional traction drive using a plurality of electric traction motors each coupled in driving relationship to a respective one of the driven axles of the locomotive. A traction power controller controls the traction motors using power from an on-board battery. A generator driven by the gas microturbine is electrically connected to the battery for maintaining the battery in a charged state. The generator and associated gas turbine is controlled in response to the state of charge of the battery. FIG. 1 illustrates the power system of the '639 patent in which a locomotive wheels 12 are driven by electric traction motors 14. Electric power for the traction motors is supplied by storage battery 16 and controlled by traction power controller 18 which may use pulse width modulation to regulate power in response to operator throttle and direction information. Battery 16 is charged by a microturbine generator 22 which comprises a gas microturbine 24 coupled to alternator 26. The control of the microturbine generator is handled by an onboard PLC 30 (programmable logic controller) which monitors the state of the battery charge, the ambient temperature and has a clock/calendar for battery equalization. As the battery approaches its gassing voltage, which represents a high state of charge, the microturbine generator shuts down. Conversely, as the charge of battery 16 drops below a certain level the microturbine is started. A high state of charge will occur only for battery equalization maintenance when all the cells are brought up to full charge. Thus, the microturbine 24 is sized so that it will run under a constant load at the maximum power output for a sustained period of time. Auxiliary loads draw from the battery charge source at a nominal 600 V DC which is converted by an inverter 32 to 480 V AC to run the locomotive's air compressor 34, traction motor blowers 36 and a 75 V battery charger 38, which is used to charge a 64V battery for powering controsl and lighting.
The system disclosed in the '639 patent is designed for yard switcher locomotives which do not require long term sustained power but rather have short term power requirements that permit the continual recharging of the battery to be done by a relatively small generator. The ratio of the energy storage capacity of the storage battery 16 to the charging power source 22 is important to minimize the cost, fuel consumption and emission of pollutants of the microturbine 24. The ratio of energy storage in kwH to the charging power in kW can be expressed as a number of hours. The optimum performance of the disclosed system is stated to be an 8 hour charging rate period or longer, representing a maximum of 125 kW of charging power per 1000 kwH of battery storage. Ideally the microturbine in these situations will be operating continuously for a period of at least ½ hour, and preferably without stopping, i.e., continuously for 100 hours or more.